Production of Alcohols from Cellulose by Supercritical Methanol Depolymerization and Hydrodeoxygenation

Abstract

The reaction pathway and products of cellulose supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHDO) were investigated. Monoalcohols, diols, alcohol ethers, and methyl esters were produced from cellulose at 300 °C with a CuMgAl mixed metal-oxide catalyst. Timecourse experiments show that cellulose is rapidly solubilized and depolymerized within 1 h with C 2 −C 4 diols being intermediates. Experiments with glucose-13 C 6 show that methanol is incorporated in all liquid products accounting for approximately 30−40% of the carbon in these products. Experiments with model compounds (dihydroxyacetone, isosorbide, and 5-hydroxymethylfurfural) indicate that the reaction pathway for cellulose occurs primarily through retroaldol condensation of solubilized cellulose followed by recondensation with methanol. Methanol produces H 2 , CO, and CO 2 through reformation with 30% of the generated H 2 being incorporated into the liquid products. Analysis of the liquid products with Fourier transform ion cyclotron resonance MS (FT-ICR MS) measured C 7 −C 12 partially oxygenated species with 2−6 double bond equivalence which could not be detected via gas chromatography (GC). We conclude that the reaction pathway occurs through rapid solubilization and depolymerization of cellulose followed by retro-aldol condensation to C 2 −C 4 oxygenates. Retro-aldol condensation products undergo hydrodeoxygenation and extensive carbon−carbon coupling to produce C 2 −C 7 alcohols or other oxygenates.

Investigation of the Reaction Pathways of Biomass‐Derived Oxygenate Conversion into Monoalcohols in Supercritical Methanol with CuMgAl‐Mixed‐Metal Oxide

“…Reactions were run with high pressure batch reactors made from Swagelok unions with ab leed valve for gas analysis. [23] These reactors are used in similar high pressure biomass conversion processes in the literature and were used in this study to maintain consistency between reaction systems. [8,37] During at ypical reaction, ar eactor is put in as and bath preheated to 300 8C.…”

“…The carbon yields are above 100 %b ecause of methanol incorporation into the products. [23] The carbon yield to total detectable products increased from 90t o1 19 %and the selectivity to monoalcohols increased from 28t o4 8% after prereducingt he catalyst. The selectivity to diols decreases after prereduction from 24 to 14 %a nd selectivity to esters and ethers remaine ssentially constant.R eactions with calcined catalysta fter eight hours reaction time had lower carbon yield and product selectivity than the prereduced catalyst.…”

“…Our previous study showed that SCM-DHDO of cellulose produces high MW species that are not detectable by GC analysis. [23] In this study we are only reporting the yield and selectivity of GC-detectable products.…”

“…Catalyst was prepared using co-precipitation according to literature. [7,23,[41][42][43] In at ypical synthesis a1 50 mL solution of DI water containing 0.06 mol of Mg(NO 3 ) 2 ·6(H 2 O), 0.025 mol of Al(NO 3 ) 3 ·9(H 2 O), and 0.015 mol of Cu(NO 3 ) 2 ·3(H 2 O) was added to a 187.5 mL solution of DI water containing 0.025 mol of Na 2 CO 3 over the course of 1hat 60 8C. The pH was kept at 10 by addition of a 250 mL 1 m NaOH solution.…”

“…The reaction also produced high molecular weight species that varied between C 7 to C 25 with two to four oxygen atoms and four to 12 double-bond equivalents. [23] Although our research showed that retroaldol condensation is an intermediate step during conversion of cellulose, we do not yet understand the subse-Reactionp athways for the conversion of cellulose into C 2 -C 6 monoalcohols by supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHDO)o veraCuMgAlo xide catalyst have been elucidated using ar ange of model compounds. SCM-DHDO of intermediate oxygenates includingg lycerol, methyl lactate, and1 ,2-ethanediolp roduces similarp roducts as those produced from the SCM-DHDO of cellulose.…”